This invention is concerned with sewing machines, more particularly, with a device for initially positioning a travelling buttonhole foot utilized for accomplishment of a one step buttonhole, into a proper position.
It is known in the prior art, to use presser devices for sewing buttonholes in which a portion of the presser device clamps the work material and travels therewith during the accomplishment of the buttonhole. Such a device is shown in U.S. Pat. No. 3,877,403 issued on Apr. 15, 1975 to Ketterer. In that patent there is disclosed a buttonhole presser device having a presser foot which may be connected to a presser bar and carry slidably thereon a work engaging shoe. The work engaging shoe is attached to the presser foot by a spring, for example, so as to have a preferred position with respect thereto.
In operation, the above described buttonholing presser foot was spring biased to an initiating position so that when an operator lowered the presser foot, the entire assembly was in its initiating position. Actually, it frequently became necessary to reposition the work material, which repositioning was sometimes accomplished by an operator by tugging thereupon. Quite frequently the effect was that the buttonhole foot was moved away from its initiating position with the result that an improper buttonhole could be effected wherein the initial bartack was not in the proper position causing an overlap or a short fall of the buttonhole legs to the bartack. An attempt to solve this problem was disclosed in U.S. Pat. No. 4,181,087 issued on Aug. 11, 1978, to Brauch et al in which, prior to initiating stitching upon a buttonhole, operation of the needle bar was suspended and operation of the feed system took place in a direction to place the work engaging shoe of the buttonhole in its initiating position. If the work engaging shoe was already in its initial position, there would only be slippage between the work engaging shoe and the feed dog. As a matter of practicality, however, a limit had to be placed on the amount of feed steps taken to place the work engaging shoe in its initiating position. If the buttonhole foot is mispositioned more than the selected number of feed steps from the mechanical backstop a partially open buttonhole will be stitched. In most cases, this mistake is not noticed until the buttonhole is almost completed, leaving a difficult thread removal job and a question in the operator's mind as to whether the machine is defective.
What is required is some means for actuating the feed system in the right direction for just that amount of time necessary to place the work engaging shoe in its initial position as the first step to the manufacture of a buttonhole.